The present invention relates to a process for the neat hydrogenation of 4-acetoxyacetophenone in the production of 4-acetoxystyrene. The invention also pertains to a process for the polymerization, and hydrolysis thereof.
It is known in the art to produce monomers, homopolymers and copolymers of 4-acetoxystyrene and to hydrolyze the same to produce 4-hydroxystyrene derivatives or poly(4-hydroxystyrene). Such find use in the production of adhesives, coating compositions, photoresists and the like. The monomeric acetoxystyrene finds use as an intermediate in the production of such polymers as poly(4-acetoxystyrene) and poly(4-hydroxystyrene). These later compounds are useful as binder resins for photoresists. Alpha acetoxystyrene and beta acetoxystyrene are known per se and are described in U.S. Pat. No. 4,144,063 and acetoxymethylstyrene is taught in U.S. Pat. No. 3,963,495. U.S. Pat. No. 4,075,237 describes 1,4-dimethyl-2-hydroxystyrene, while U.S. Pat. No. 4,565,846 teaches the use of poly(3,5-dimethyl-4-hydroxystyrene).
Japanese patent 84023747 describes anti-static compounds employing poly-acetoxymethylstyrene and U.S. Pat. No. 4,221,700 describes a stabilized synthetic polymer composition using poly(alkylated alkenylphenol) including 2-methyl paravinyl phenol. U.S. Pat. Nos. 4,600,683 and 4,543,397 describe poly (alphamethyl vinylphenol). U.S. Pat. Nos. 4,517,028; 4,460,770 and 4,539,051 describe dimethyl vinyl phenol. The preparation of 4-hydroxystyrene is well known in the art. One process is described in U.S. Pat. No. 4,316,995 and another is described in U.S. Pat. No. 4,451,676.
Vinyl phenol may be prepared by a five step process of (1) acetylating phenol to p-hydroxyacetophenone, (2) acetylation of p-hydroxyacetophenone to p-acetoxyacetophenone, (3) hydrogenation to p-acetoxyphenyl methylcarbinol, (4) dehydration to p-acetoxystyrene, and (5) saponification to p-vinylphenol. The method is more fully described in Corson, B. B., et al, Preparation of Vinylphenols and Isopropenylphenols, J. Org. Chem., April 1958.
The prior art process for the hydrogenation of 4-acetoxyacetophenone to acetoxyphenyl methylcarbinol has been conducted with a Pd/C catalyst. However, this method has required the presence of such solvents as methanol and tetrahydrofuran. The required use of the solvent has been a problem in practice of this process Problems which have been experienced include the dissolution of the 4-acetoxyacetophenone in the solvent; increased reactor volume due to the presence of the solvent; subsequent removal of the Pd/C catalyst from the large volume of solvent in the 4-acetoxyphenyl methylcarbinol mixture; separation of the solvent from 4-acetoxyphenyl methylcarbinol; purification and recycling of the solvent; solvent losses; and by-products from the solvent. The present invention employs a process wherein the solvent is completely eliminated. It has been surprisingly found that the selectivity of the reaction is substantially not adversely affected by the elimination of the solvent component. Also, surprisingly other side reactions are not observed and an economical operation of the process is made possible.